Water Supply in Times of Climate Change — Tracer Tests to Identify
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Water supply in times of climate change — Tracer tests to identify the catchment area of an Alpine karst spring, Tyrol, Austria Schäffer, Rafael; Sass, Ingo; Heldmann, Claus-Dieter (2020) DOI (TUprints): https://doi.org/10.25534/tuprints-00013341 Lizenz: CC-BY-NC 4.0 International - Creative Commons, Namensnennung, nicht kommer- ziell Publikationstyp: Artikel Fachbereich: 11 Fachbereich Material- und Geowissenschaften Zentrale Einrichtungen Quelle des Originals: https://tuprints.ulb.tu-darmstadt.de/13341 Arctic, Antarctic, and Alpine Research An Interdisciplinary Journal ISSN: 1523-0430 (Print) 1938-4246 (Online) Journal homepage: https://www.tandfonline.com/loi/uaar20 Water supply in times of climate change—Tracer tests to identify the catchment area of an Alpine karst spring, Tyrol, Austria Rafael Schäffer, Ingo Sass & Claus-Dieter Heldmann To cite this article: Rafael Schäffer, Ingo Sass & Claus-Dieter Heldmann (2020) Water supply in times of climate change—Tracer tests to identify the catchment area of an Alpine karst spring, Tyrol, Austria, Arctic, Antarctic, and Alpine Research, 52:1, 70-86, DOI: 10.1080/15230430.2020.1723853 To link to this article: https://doi.org/10.1080/15230430.2020.1723853 © 2020 The Author(s). Published with license by Taylor & Francis Group, LLC. Published online: 11 Mar 2020. Submit your article to this journal Article views: 215 View related articles View Crossmark data Full Terms & Conditions of access and use can be found at https://www.tandfonline.com/action/journalInformation?journalCode=uaar20 ARCTIC, ANTARCTIC, AND ALPINE RESEARCH 2020, VOL. 52, NO. 1, 70–86 https://doi.org/10.1080/15230430.2020.1723853 Water supply in times of climate change—Tracer tests to identify the catchment area of an Alpine karst spring, Tyrol, Austria Rafael Schäffer a, Ingo Sassa,b, and Claus-Dieter Heldmanna aInstitute of Applied Geosciences, Geothermal Science and Technology, Technische Universität Darmstadt, Darmstadt, Germany; bDarmstadt Graduate School of Excellence Energy Science and Engineering, Technische Universität Darmstadt, Darmstadt, Germany ABSTRACT ARTICLE HISTORY Climate change and glacial retreat are changing the runoff behavior of Alpine springs and Received 20 June 2019 streams. For example, in the extremely dry and hot summer of 2018, many springs used for Revised 18 December 2019 drinking water supply lost up to 50 percent of their average discharge; a few springs have even Accepted 23 December 2019 run dry. In order to ensure drinking water supply in the future, springs featuring large and KEYWORDS constantly sufficient discharge rates will have to be identified and tapped. A case study was Uranine; karst; discharge/ undertaken at the Tuxbachquelle because catchment area and temporal variation of physico- runoff; rock glaciers; chemical and hydrochemical properties were previously unknown. Tracer tests with uranine Hochstegen Formation proved a hydraulic connection between this karst spring and a stream a few kilometers uphill. At low runoff, uranine needed about 4½ hours from the sink to the spring, whereas at high runoff more than four days was required. It became evident that discharge, electrical conductivity, temperature, and turbidity of the Tuxbachquelle respond within a few hours to precipitation events. The water quality and an examination of the water balance resulted in a significantly larger catchment area. It is assumed that widely karstified calcite marble subterraneously drains a considerable part of the Tuxertal (Tux Valley), including some active rock glaciers. Introduction dominantly situated (Lambrecht and Kuhn 2007). With respect to the catchment areas of big Alpine rivers, such Motivation as the Rhône, Rhine, or Inn, the contribution of glacier melt The importance of glaciers and rock glaciers as water reser- reaches up to 25 percent of the total summer runoff (Huss voirs and for hydropower generation should be reevaluated 2011). Small catchment areas of several square kilometers for the future. Between 1850 and 2011, glaciers in the can derive their runoff almost completely from meltwater. Zillertal Alps lost about two thirds of their area (Fischer Permafrost and dead ice melt may add significant propor- et al. 2015). Within the Tuxertal (Tux Valley), the glacier tions and influence water composition (Winkler et al. 2016; area reduced from 20.6 km2 to 7.1 km2 between 1850 and Colombo et al. 2018; Brighenti et al. 2019). 2004 (Pröbstl and Damm 2009). Based on the latest Almost all active rock glaciers in eastern North Tyrol Tyrolean Geographic Information System (tiris) orthopho- are located in the Tuxertal. The area of these active rock tos of 2016 (Tyrolean Geographic Information System glaciers in the Tux Alps is estimated at 2.2 km2.The 2019), the glacier area totals only 5.2 km2.Thelossofglacial surface of another 230 inactive or fossil rock glaciers area and volume depends on several factors. Though no amounts to 9.1 km2 (Krainer and Ribis 2012). Active losses or slight glacier advances were observed in the 1970s rock glaciers can feature daily varying influences on dis- and 1980s, there has since been a significantly accelerating charge rates, chemical compositions including heavy glacier retreat (Gross 1987; Schwendiger and Pindur 2013; metal concentrations, and physical properties of down- Fischer et al. 2015). Minor glaciers smaller than 2 km2 are stream streams and springs (Krainer and Mostler 2002; much more affected by the decline than larger glaciers Thies et al. 2013; Nickus, Thies, and Krainer 2015). (Schwendiger and Pindur 2013).Icelossoccursmainlyat The Alps are more strongly affected by climate altitudes lower than 3,200 m. a.s.l., where small glaciers are change than other regions (Auer et al. 2007; Brunetti CONTACT Rafael Schäffer [email protected] Institute of Applied Geosciences, Geothermal Science and Technology, Technische Universität Darmstadt, Schnittspahnstrasse 9, Darmstadt 64287, Germany. © 2020 The Author(s). Published with license by Taylor & Francis Group, LLC. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. ARCTIC, ANTARCTIC, AND ALPINE RESEARCH 71 et al. 2009). It can be demonstrated that climate change nappe stacking. A more detailed description of the has led to significant changes in precipitation and the geological setting is given in Schäffer et al. (2018). runoff behavior of rivers during recent decades The Tuxbachquelle (TQ) is situated within the 4-km- (Brunetti et al. 2006; Saidi et al. 2018). In addition, long and up to 60-m-deep gorge of the Tuxbach (Tux small catchment areas react immediately to weather Creek) next to Finkenberg (Figure 1). extremes, such as the expected increase in heavy rainfall The Tuxbachquelle originates in the Jurassic events or longer dry periods caused by climate change Hochstegen Formation. The structural strike is about (Rajczak, Pall, and Schär 2013). It is therefore to be 60° ENE parallel to the valley and dips approximately expected that springs at high elevations will be subject 70° NNW. From base to top, the Hochstegen Formation to larger discharge fluctuations and will dry out more contains thin layers of quartzite, phyllite, and brownish frequently in the future. Climate models predict a time marble, followed by sequences of grayish-blue banded shift of the precipitation maxima from summer to calcitic and dolomitic marbles. Within the footwall of winter as well as that precipitation will more often be the Hochstegen Formation, the topographically higher in the form of rain instead of snowfall (Gobiet et al. Ahorn Gneiss is exposed (Figure 1). It consists of ortho- 2014). The resulting change in runoff characteristics gneisses, which are primarily augen gneiss. The contact will be superposed by earlier snowmelt and a decrease between both units is described as autochthonous, par- in snow cover, especially below 2,000 m (Kobierska autochthonous, or allochthonous (Frisch 1968, 1980; et al. 2013; Gobiet et al. 2014). Because the demand Thiele 1976). Low mineralized, lime-unsaturated, and for electricity in winter is higher than that in summer, cold waters from the Ahorn Gneiss infiltrate the this effect is advantageous for hydropower production Hochstegen Formation, having a high karstification (Wagner et al. 2017). On the other hand, this is dis- potential (Sass, Heldmann, and Schäffer 2016). advantageous for the water supply, because in Austrian The Tuxertal is rich in caves like other regions of rural and tourist regions water consumption is Austria built by calcareous rocks (Christian and Spötl increased by 40 to 120 percent during the summer 2010; Spötl, Plan, and Christian 2016). Almost forty period (BLFUW 2012). caves are known in the middle and upper parts of the The water supply in rural Austria is largely in private valley, and the ongoing glacier retreat has allowed new hands. Tributary valleys of the Zillertal are character- discoveries in recent years (Spötl 2009). There are two ized by isolated single spring or single well water sup- recently gauged and officially catalogued caves within plies. Typically, they have small catchment areas or the Tuxbach gorge. Goldbründl cave, located 35 m hydraulic connections to fissures, fractures, and faults. above the Tuxbach level, is at least 14 m long and To provide a reliable water supply, it is necessary to tap 8 m deep and shows a very variable water level at its perennial springs with a sufficient long-term discharge lower end of at least 20 m (Spötl and Schiffmann 2014). rate. It is suspected that many small catchment areas The mouth of the Goldbründl into the Tuxbach is will not fulfill this requirement due to ongoing climatic located close to TQ-12 (Figure 2). Grabungshöhle is change. Although the Tuxbachquelle has been identi- situated about 50 m further east, with a length of at fied by water authorities as important for future water least 31 m and a depth of 12 m (Spötl and Schiffmann supplies, this spring has never been thoroughly inves- 2014).